It is common practice to dispense semi-liquid substances such as creams, lotions, or pastes by means of a metering pump mounted in sealed manner on a supply of such a substance and actuated by means of a pusher. This provides numerous advantages in the food industry, the pharmaceutical industry, or even in the cosmetic industry, with the advantages including the possibility of dispensing predetermined quantities, guaranteeing clean delivery, facilitating emptying of the supply, . . . . However, problems remain which are related to the conventional design of dispenser heads constituted by a pusher and a pump.
The pump generally communicates with a delivery orifice formed in the pusher by means of a channel situated downstream from the outlet valve of the pump chamber. Thus, once the head has been actuated for the first time, this channel is filled with substance. The quantity of substance occupying the corresponding dead volume is thus in contact with ambient air. If there is a pause of any length of time before the next actuation, then the substance retained in this way begins to dry and harden. The dispenser then becomes unusable since the contents of the outlet channel block the path to the outside. Depending on the nature of the substance, other difficulties may also be expected with this volume exposed to the air. For example, the substance therein may oxidize and lose its properties. If the substance is a medicine, contamination by the bacteria present in the water vapor of the environment may make the substance harmful.
In order to avoid these problems, various systems have been proposed. Some consist in removing all of the substance remaining in the outlet channel at the end of head actuation. This is achieved in the prior art, for example, by forcing the contents of the channel into an intermediate chamber which is closed by a valve which allows flow to take place in both directions. The valve is then advantageously constituted by a relatively resilient disk provided with one or two small slots. Other systems seek to close the delivery orifice itself as soon as a dose of substance has been delivered. To this end, European patent application EP-A-0 129 643 filed in 1984 by Pfeiffer has a needle which is fixed to a pair of pistons. The needle occupies the outlet channel and in the rest position it co-operates with the delivery orifice which then acts as a valve seat, whereas during dispensing, the pressure of the substance causes the pair of pistons to retract into the channel.
These prior inventions suffer from the drawback of giving rise to parts which are relatively complex in shape: in one case an intermediate chamber with a valve, and in the other case a pair of pistons. Unfortunately, these parts are very small in size since they have to occupy the outlet channel of a dispenser head (no more than a few millimeters). Consequently they are expensive to make. In any event, the operation of this type of internal valve is unreliable.
French patent FR 1 539 302 avoids this type of drawback by taking advantage of the deformability of a flexible shutter. However it is implemented by means of a resilient "sheet" or "membrane" disposed in front of the dispensing head outlet and perforated by a hole or a slit. So long as the membrane is retained by a ring wedged in the bottom of a cylindrical housing formed in the head, then the substance delivered under pressure distends the membrane and its hole or slit is thus opened. When the pressure is removed, the lips of these perforations come back practically into contact. Although the simple operating principle ensures that closure takes place effecively, installing such a membrane is difficult and hardly compatible with maintaining the production rates that are required if such dispensing heads are to be reasonably priced.
The present invention therefore seeks to avoid problems relating to a volume of substance remaining in the outlet channel and exposed to air, but by means of a part which is simple in shape and which enables a dispenser head to be made for semi-liquid substances which is both cheap and reliable.